A known structure of a separator used for fuel cells is configured to have concavo-convex structures formed in a mutually reversed relation on two opposed sides thereof and define flow paths of different fluids on the respective sides (see, for example, Japanese Patent Laid-Open No. 2003-142126). Holes for defining manifolds of supplying and discharging a fluid from and to the corresponding side of the separator are generally provided in an outer circumferential area of the separator. The flow path formed on each side of the separator is thus designed to have a specific shape for communicating a supply manifold and a discharge manifold of the corresponding fluid and introducing the fluid on the side of the separator. The relevant prior art techniques have been disclosed in Japanese Patent Application No. 2006-519715 (International Publication No. 06/075786) and Japanese Patent Laid-Open No. 2005-108505.
The layout of a supply manifold and a discharge manifold of each fluid is determined according to various factors. In some layout of the fluid manifolds, there may be a non-uniform flow rate distribution of the fluid in the fluid flow path formed on the side of the separator. In the separator configured to have the concavo-convex structures in the mutually reversed relation on the two opposed sides thereof, the shape of the fluid flow path formed on each side is restricted by the shape of the concavo-convex structure for defining the fluid flow path on the other side. The mutual restriction of the shapes of the concavo-convex structures on the opposed sides of the separator makes it difficult to solve the non-uniformity problem of the flow rate distribution of the fluid caused by the layout of the fluid manifolds. Equalization of the flow rate distribution of the fluid is accordingly required in the separator configured to have the concavo-convex structures formed in the mutually reversed relation on the two opposed sides thereof.